1. Field of the Invention
This invention relates to an ionization smoke detector device or system, and more particularly, to improvements in the operation of that class of smoke detector devices which are arranged to have a radioactive source and at least one ionization chamber irradiated by such source.
A variety of ionization smoke detectors have been developed over the past several decades. One form of such detector includes a pair of ionization chambers connected in series between the terminals of a voltage source and each having a pair of electrodes and a radioactive source in each chamber. Typically, one chamber is open to the ambient atmosphere so as to allow smoke to enter; this is sometimes referred to as the open chamber; while the other chamber is closed to the ambient.
Another type or form of ionization smoke detector provides for a single ionization chamber subdivided into two regions, with one of the regions, which is defined by an intermediate electrode and an outer electrode, having a much greater volume than the other region, which is defined in common by the same intermediate electrode and by an inner electrode.
In either type of smoke detector noted above, it is conventional to provide a field effect transistor having a gate electrode connected to the intermediate electrode located at the junction between the chambers or regions; and to have the source-drain conduction path connected between the terminals of a voltage source, which is also connected across the inner and outer electrodes of the detector. The field effect transistor operates to sense a potential change at the junction of the two chambers or regions so that when smoke enters the detector chamber, the change of potential resulting from a change of impedance in the chamber, causes substantial sourcedrain conduction of the field effect transistor. The transistor conduction, in turn, triggers an alarm device to give a suitable indication of the presence of smoke.
2. Background Art
In order to appreciate the objects and purposes of the present invention, reference may be made to the following U.S. Pat. Nos. considered useful in providing background information: 3,935,466; 3,935,492; 4,044,263.
What has been lacking in the prior art ionization devices is a suitable means or arrangement for providing complete control over the detector or alarm system. That is to say, for controlling and selecting a range of potentials over which a suitable signal can be given to produce an alarm output.
Another deficiency that the present invention is directed to overcoming is the lack of a means for efficiently and thoroughly testing the operation of the detector system so as to insure that the system is in good working order. In other words, one wants to be able to simulate the presence of smoke so as to determine whether or not the system will work efficiently should a smoke condition occur in the atmosphere.
Accordingly, the principal objects of the invention are to provide selective control of the triggering point for the alarm system and effective testing of the system.